An image forming apparatus performs an image forming process by receiving toner from a toner cartridge and then forming a toner image on a photosensitive drum. The image forming apparatus ultimately transfers the toner image from the photosensitive drum onto a print medium.
The image forming apparatus calculates an amount of toner supplied to the image forming apparatus from a toner cartridge (toner delivery amount), based on an amount of time toner replenishment motor is driven (the toner replenishment time) to rotate an auger or screw that delivers toner from the toner cartridge to image forming device or by evaluating image density (or number of pixels). The image forming apparatus determines when the amount of toner in the toner cartridge is low based on a sum of toner delivery amounts and the storage capacity of the toner cartridge.
However, there may be a difference between the calculated toner delivery amount(s) and the amount of toner actually supplied from the toner cartridge due to factors such as the screw rotating inertially after the toner replenishment motor stops, variations in toner flowability, toner transfer efficiency, and variations in the amount of toner actually delivered by the auger or screw. As a result, there is a problem that an output based on remaining toner levels (for example, a toner near empty indication) may not be accurate.